A familiar system, which is taken as a point of departure in the formulation of the general sense of Patent claim 1, includes an initial polarization splitter/combiner element, which splits the oncoming signal into two signals with mutually perpendicular polarization directions; a delaying unit, which is installed in one of the signal paths of the two (split) signals; and a second polarization splitter/combiner element, which reunites the two severed signals.
This familiar system has the disadvantage that it allows only the compensation of first-degree PMD-induced distortions. However, it is precisely in long transmission paths that second-degree PMD-induced distortions play a considerable role.
Another known system for PMD emulation is, for instance, a system of PM fibers with various or equal group running times, on which a polarization transformation unit is superposed in each case.